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  • Burnt Forward clutch
  • Poor shift quality
  • Wrong gear starts
  • Delayed engagement


The 1-2 accumulator piston wears at the pin bore due to contact with the steel pin.


Sonnax accumulator piston has a longer pin contact surface area to reduce wear on the piston and prevent cocking.

3T40 (125C)

Accumulator Piston Kit
Part No. 75921-01K

View Instructions

GM vehicles with 125 or 3T40 transmissions may have problems with burnt forward clutches, delayed engagements, poor shift quality or wrong gear starts due to loss of oil pressure through the accumulator circuits and worn piston pin bore. Continuous oscillation and spring loads cause the piston to wear or cock in the housing. This allows fluid to cross leak into other circuits and the piston to cock in the bore. The Sonnax accumulator piston kit 75912-01K has a larger piston-to-pin contact area to reduce wear and prevent cocking.

Sonnax also offers an oversized accumulator pin and reamer kit 75921-03K that allows the OE piston to be salvaged.

• Longer piston pin contact surface area reduces wear on the piston and prevents cocking

• Piston increases the preload on the accumulator spring for firmer shifts

  • Piston
  • Pin
  • 75921 01k combo
  • 75921 01k